In constructing tunnels, arches or the like, a suitable opening is excavated. As excavation proceeds, it is usually necessary to provide support in order to prevent cave-ins and carry the weight bearing on the tunnel. Wooden beams were formerly used for support; however, in more recent years, the preferred structures are tunnel liners made from metal and preferably steel plates. A tunnel liner plate is typically a four-sides structure, having a generally rectangular configuration, having two longitudinally extending sides and two transversely extending ends, and is curved in the longitudinal direction to conform to the curvature of the tunnel being lined. As tunneling progresses, it is common practice to install the liners ring by ring just behind the forward end of the tunnel. A ring of tunnel liner plates is an assemblage of plates joined together end to end and extending around the circumference of the tunnel. Successive rings or courses of tunnel liner plates are typically arranged in off-set fashion similar to successive courses in a brick wall.
The most common cross-sectional shape of a tunnel is circular (or approximately circular), and so tunnel liner plates commonly have an arcuate or circular curvature in the longitudinal direction and typically no curvature in the transverse direction. However, other cross-sectional shapes of tunnels, as for example, are typically more than 180 degrees but less than 360 degrees, ("arcuate" denoting any part of a true circle), semi-circular, and horse-shoe shape.
A tunnel liner plate may have inwardly extending flanges along both its sides and ends, or along its sides only, said flanges typically having bolt holes so that adjacent liner plates can be bolted together to form a tunnel liner.
U.S. Pat. No. 1,967,489 to White shows a representative tunnel liner. The tunnel liner plate illustrated therein is constructed of plate metal, provided with inwardly extending flanges along both its side edges and its end edges, with bolt holes in all flanges. The main portion or body wall of the plate is provided with a pair of spaced longitudinally extending ribs for reinforcement. These ribs stand out from the outer face of the body wall and comprise transversely flat (and longitudinally curved) facing walls.
The neutral axis of the liner plate in U.S. Pat. No. 1,967,489 is illustrated in FIG. 3 thereof. Every tunnel liner plate has a neutral axis, which extends from side to side as shown in FIG. 3 of the White patent. The center of mass of the liner plate is located along the neutral axis.
U.S. Pat. No. 2,114,834 to Foukal shows a tunnel liner plate having side and end flanges with bolt holes therein, and provided with a thrust member in the form of a corrugated plate that is curved to conform to the curvature of the liner plate 4, and which has corrugations extending from side to side of the liner plate. The corrugated plate may be secured to the liner plate by welding the lateral edges of the former to the side flanges of the latter. Foukal also illustrates the formation of a ring of liner plates, by bolting adjacent plates together along their respective end flanges.
U.S. Pat. No. 3,357,194 to Fisher shows a tunnel liner plate which, in transverse cross-section, comprises a relatively flat central portion, corrugations on either side thereof, and side edge flanges which are disposed essentially parallel to the central portion of the liner plate, rather than at right angles thereto. One of these flanges, "the leading edge flange" (this term being used with reference to the tunneling direction) is disposed outside the neutral axis and the other, the "trailing edge flange", is disposed inside the neutral axis as shown in FIG. 2. Additional supporting members in the form of removable channels, I-beams (the form shown in the drawing) or H-beams may be provided. Patentee states that his tunnel liner plate, by virtue of his flange structure, is capable of being stored more compactly and is easier to install than a tunnel liner plate having either two or four inwardly extending flanges provided with bolt holes. Patentee also states that his tunnel liner plate requires less weight of material in relation to strength.
Most tunnel liner plates continue to have either two or four inwardly extending flanges which are disposed along the edges of the liner plate (or more specifically the outer wall thereof), as shown for example in U.S. Pat. No. 1,967,489 to White, cited supra.
Meanwhile, the art continues to look for a liner plate having a more favorable strength to weight ratio than that afforded by a conventional flanged liner plate such as that shown in the White patent.